The present disclosure relates to an organic EL (Electro Luminescence) display device that relies on the phenomenon of organic electroluminescence to emit light and a manufacturing method of the same.
The advancement of the information and telecommunication industry at an accelerating pace has led to demand for display elements offering sophisticated performance. Among these, the organic EL element that is attracting attention as a next generation display device features not only a wide view angle and excellent contrast but also quick response time.
The light-emitting layer and other layers forming an organic EL element are broadly classified into two types, namely, low and high molecular weight materials. It is commonly known that low molecular weight materials offer higher light emission efficiency and longer life. In particular, low molecular weight materials offer higher blue light performance.
In order to form an organic film, on the other hand, a dry method (vapor deposition method) such as vacuum vapor deposition is used for low molecular weight materials, and a wet method (coating or printing method) such as spin coating, ink jet or nozzle printing is used for high molecular weight materials.
The vacuum vapor deposition method is advantageous in that the process step adapted to remove the solvent is not necessary after the film formation because it is not necessary to dissolve the material adapted to form an organic thin film in the solvent. However, patterning using a metal mask is difficult. In particular, the equipment and manufacturing cost adapted to produce large-size panels is high. As a result, the method has drawbacks including its difficulty in applying the method to large-screen substrates and problem with achieving volume production. For this reason, the wet methods such as ink jet and nozzle printing are drawing attention for their relative ease in increasing the display screen size.
However, the blue light-emitting material in particular of all the high molecular weight materials used in ink jet or nozzle printing offers low emission brightness and short life, thus making it difficult to manufacture practical display products using a wet method.
Therefore, in Japanese Patent Laid-Open No. 2007-73532 (hereinafter referred to as Patent Document 1), for example, a manufacturing method is proposed in which red and green light-emitting layers are patterned for each pixel using ink jet, after which a blue light-emitting layer is formed on top thereof by vacuum vapor deposition.